Automatic controlled electrostatic coating apparatus



March 11, "1958 A. s. DAVIS, JR

AUTOMATIC CONTROLLED ELECTROSTATIC COATING APPARATUS 3 Sheets-Sheet 1 Filed May 6, 1955 w \ZZI...

o o h $30 EsEH NEED m QZOumw LQQ INVENTOR ALBERT S. DAVIS JR ATTORNEY March 11, 1958 A. s. DAVIS, JR 2,825,166

AUTOMATIC CONTROLLED ELECTROSTATIC COATING APPARATUS Filed May 6, 1955 3 Sheets-Sheet 2 INVENTOR ALBERT S, DAVIS JR.

ATTORNEY March 11, 1958 A. s. DAVIS, JR 2,826,166

AUTOMATIC CONTROLLED ELECTROSTATIC COATING APPARATUS 5 Sheefs-Sheet 3 Filed May 6, 1955 T INVENTOR 51' ABERT s. DAVIS JR.

ATTORNEY AUTOMATIC CONTROLLED ELECTROSTATIC COATING APPARATUS Albert S. Davis, Jr., Somerville, N. 1., nssignor to Research Corporation, New York, N. Y., a corporation of New York Application May 6, 1955, Serial No. 506,610

Claims. (Cl. 118-5) above process, and to provide an improved apparatus therefor, by depositing the coating material in finely divided form under the influence of an electrostatic field on the material to be treated, and by electronically heating the material to the exact degree required, under precise and automatic control.

Another object of the invention is to remove electrostatic charges produced on the fabric by the preceding treatment and to exactly neutralize such charges, so that the material may be rolled up or otherwise further treated without the accumulation of dangerous or bothersome static charges.

A further object of the invention is to provide improved means for detecting at successive stages along the path of travel of the fabric, the amount of moisture remaining in the fabric, and applying instantaneous, electrically controlled heat so as to remove all of the undesired moisture Without danger of injuring the fabric by excessive heat.

Still another object is to provide means for detecting the amount of electrostatic charge on the fabric after it has been treated, and for precisely neutralizing such charge so as to leave the fabric in uncharged condition.

The specific nature of the invention, as well as other objects and advantages thereof, will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings, in which:

Fig. 1 is a schematic block diagram showing the arrangement of the different components of the treating system according to the invention;

Fig. 2 is a diagrammatic view and circuit diagram of a sprayer unit of the invention;

Fig. 2a is a plan view showing the arrangement of the spraying heads across the width of the sheet or web being treated to insure uniform deposition of finishing solution thereon;

Fig. 3 is a schematic View of a heating section, using electric diathermy to heat the fabric;

Fig. 4 is a schematic diagram showing the energizing circuit for the heating electrodes of the primary heater;

Fig. 5 is a circuit diagram of the oscillator circuit for energizing the heating electrodes;

Fig. 6 is a schematic circuit diagram of the heating and control circuit for the secondary heating electrodes; and

Fig. 7 is a circuit diagram of the static discharger for automatically neutralizing any static charge on the fabric.

Referring to Fig. 1, the web or sheet of material to be treated 2, is in the form of a continuous sheet of a defininited States Patent 0 fabric into the treatment area shown in Fig. 1.

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tive width and it is assumed to reach the apparatus in dyed condition and ready for finishing. Rollers 3 driven by an external source of power (not shown) move the At station A, the fabric is suitably electrostatically coated with material as will be described in more detail below; staticn B represents a primary drier for primary heating of the fabric to drive off most of the entrained moisture, while stations C and D represent secondary driers which are combined with moisture-sensing systems to insure complete drying of the fabric without overheating it. Station B shows a static neutralizer system for neutralizing or discharging static charges left on the fabric by the preceding treatment, which are often bothersome and often dangerous since they tend to accumulate on the final roll of material until they reach dangerous proportions.

At station A the web 2 is suitably coated with a thermosetting short polymer or other desired coating or finishing material, the coating being applied by means of an electrostatic field to insure that all portions of the Web are substantially uniformly coated. The form of the electrostatic coating apparatus may be varied, depending on the type of material to be coated, and the nature of the Web as is well known in the electrostatic coating art. For example, a liquid coating material may be discharged into a chamber as a mist and the mist then electrostatically deposited upon the web. Suitable apparatus of this type is shown in U. S. Patent 1,788,600, I. S. Smyser. However, in the preferred form of this invention an electrostatic spray device is used essentially as shown in Wintermute Patent No. 2,221,338, and comprises a pipe or duct 6 for conducting the finishing solution under pressure to a nozzle 7 so that it is sprayed downwardly upon the fabric 2 as the latter passes beneath the spray nozzle. Preferably a series of such nozzles is provided transversely of the fabric web, as best indicated in Fi 2a. A series of attenuated electrodes 8 surrounds the nozzle 7, and are supplied through lead 9 from one terminal of a high voltage D.-C. rectifier 11, which is shown as a mechanical rectifier, but which may be of any known type. A flat plate electrode 18 is provided beneath the fabric for cooperation with electrodes 8. The electrodes are energized by means of a circuit including high voltage transformer 10, adjustable resistor 13, condenser 19 and spark gap 14 to provide impulses of steep wave front. if the spark gap 14 is shunted by switch 16, ordinary high voltage unidirectional pulsating current is provided. The material discharged by nozzle 7, in the form of a highly atomized spray, enters the zone of deposition between the opposing electrodes 8 and 13 and is deposited on the fabric 2 both by impact and by electrical deposition. The attenuated electrode members 8 provide a curtain of corona discharge surrounding the zone of deposition which effectively prevents the current of air from carrying undeposited material out of the zone of deposition. This treatment also tends to leave a large static charge on the fabric, and although some of this charge may be removed by the subsequent drying operations as Well as by the etfect of water entrained in the solution, under some conditions of operation a substantial amount of charge may be retained on the fabric web 2. Under other conditions of operations, depending upon the amount of moisture in the solution as well as upon atmospheric conditions, it is even possible for the fabric web leaving the drier zone to have acquired a charge of opposite polarity from that which it had upon leaving the sprayer zone. For this reason, in order to insure complete neutralization of all charges on the fabric before it is wound into rolls for further handling, 1 provide a novel electrostatic neutralizing means at the very end of the entire treatment areas, which will be described hereinafter.

Upon leaving the spraying area, it is necessary to heat treat the fabric both in order to set the effective component of the sprayed finish material which is typically an organic thermosetting short polymer resin, and also in order to completely drive out all of the moisture from the fabric prior to winding it into new rolls for subsequent handling. This heat treatment is usually quite critical, and has been diflicult to accomplish by prior art methods, since an excess of heat may damage either the fabric itself or the finish material, while insutlicient treat ment will produce an unsatisfactory product. I, therefore, provide a series of heating zones. The first heating zone at station B is not automatically controlled, but is manually set in advance to accomplish the major portion of the desired heating, but not all of it, so that the material leaves this zone in unfinished condition, and requires some additional heating. Since only a relatively slight amount of additional heating is now required, this can be more sensitively controlled than by attempting to perform the entire operation at the initial station. In fact, it is advantageous to use two or even more subsequent heating stations, cach controlled by a separate sensing apparatus, which will be described below, and each, therefore, successively supplying a smaller amount of additional heat than its predecessors, whereby exceedingly accurate control can be obtained without danger of injury to the material being treated. For the heating medium, it is preferred to use the action of a dielectric heating field. This is particularly advantageous because it can be readily controlled, its action is instantaneous in heating the entire bulk of the material, and it is particularly effective in heating water, because of the high dielectric constant of water, and once most of the water is driven from the fabric, further heating proceeds at a much lower rate, with consequent less danger of injury to the material. However, in some cases it would also be satisfactory to use radiant heating means.

Fig. 3 shows a preferred form of heating electrodes for use in the heating and drying section of the treater. These electrodes are preferably in the form of fiat conductive plates 21 and 22 between which a radio frequency alternating field is established in accordance with the known principles of diathermy. Rollers 23 and 2d are provided immediately outside of and in advance of the heat treating zone, and serve as the electrodes of a resistance measuring circuit in order to determine by resistance measurement the amount of moisture remaining in the material after it has passed the preceding treatment zone. An additional set of rollers 26 and 27 may be provided if desired and may be connected to the mechanical drive system to assist in transport of the fabric web 2. Rollers 23 and 24 may also be power driven if desired, or may merely be rotated by the friction of the web 2 on opposite sides of which they press.

Fig. 4 shows a typical circuit for energizing the heating electrodes 21 and 22. Three phase alternating current is supplied through a three phase voltage regulator 29 and switch 31, which may be of the remote control type, to three phase transformer 32 to supply three phase mercury arc rectifier 33, the rectified output of which is supplied to the input terminals of oscillator 35, on input leads 3 and 35. The output leads 38 and 39 of the oscillator are connected to plates 21 and 22 of the high frequency unit.

Fig. 5 shows the circuit of the oscillator, which may be a conventional Hartley oscillator. Output leads 3%; and 39 connect directly to the plates 21 and 22 as shown in Fig. 4. Lead 34 conducts direct current through the ammeter ii to the plate of triode 42. As the circuit is essentially of conventional design, it will not be described in detail. A variable condenser 43 across output loads 33 and 39 permits adjustment of the output frequency to the optimum value for dielectric heating of the parucular material being treated.

Fig. 6 shows the dryer and heater circuits for stations C and D. The supply portion of the circuit is essentially the same as in Fig. 4-, and corresponding reference numerals with a prime added are employed for this portion of the circuit. However, rollers 23 and 24 are arranged as one arm of a bridge circuit 4-6, the other arms of which are adjustable resistors as shown. Diagonal points 47 and 48 of the bridge are supplied with a suitable line voltage, which may be either direct or alternating current, and an output will be produced across the remaining diagonals 43' and 4-9 of the bridge to energize or de-energize relay 51 in accordance with the resistance between rollers 23 and 2 which may be set for any desired value corresponding to a predetermined moisture condition. If the amount of moisture remaining in the fabric after the primary drying and heating stage B is still excessive, relay 51 will be energized, and the electrodes 23 and 24 will be effected to further heat and dry the fabric web. in this way, by the addition of only a slight and readily controllable amount of heating energy, a very line and accurate control may be obtained. However, in some instances, the accuracy of control is such that it is desirable to incorporate a further subsequent stage of tertiary drying l), which will be in all respects identical to the unit C. At each stage the rollers 23-, 24,

sense the condition of the material as it leaves the preceding stage and provide additional treatment as required. It will be understood that the rollers 25, 24, or at least the one on the ungrounded side of the circuit, will be suitably insulated from the frame of the machine by insulating bushings, etc., so that it may be included as part of the electrical circuit by means of a conventional slip-ring and brush arrangement (not shown).

Fig. 7 shows the electrical static discharger. A grounded plate electrode 51' is located directly beneath the fabric web and an opposing attenuated discharge electrode 52 provides an alternating corona discharge through oppositely oriented vacuum tube triodes 53 and 54, supplied by high-voltage transformer 55. As long as the fabric carries no charge, the corona discharge is alternately positive and negative and no net neutralizing charge is added. However, the grid of each triode is separately excited from respective rollers 56 and 57 (which may alternatively be sliding brushes in contact with, or points immediately adjacent, the fabric surface), and the arrangement is such that when the fabric carries a charge, the corresponding polarity of the alternating current discharge is blocked by the voltage transferred from the rollers to the grids of the tubes, in one direction but not in the other direction whereby only a discharge of the opposite polarity is emitted at electrode 52 to neutralize the charge on the fabric. In this way, complete neutralization is obtained. It will be understood that the electrode 52 and the rollers 56 and 57 are spaced so closely together that they all act on substantially the same area of treated material.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of my invention as defined in the appended claims.

For example, other than fabric webs may be treated in the apparatus of the present invention, such as paper and other than water soluble coating and finishing solutions may be employed.

I claim:

1. Apparatus for coating a moving web with a finishing material comprising means for continuously moving said web in one direction, means for electrostatically applying a solution of said finishing material in finely divided form on web during said motion, a first heating' station extending transversely across said web and spaced in the direction of motion thereof from said electrostatic solution, applying means for supplying a substantial portion of the heat required to treat the finishing material, means for sensing the resistance to the flow of electric current through said web subsequent to leaving said first heating station, and a second heating station controlled by said sensing means for supplying additional heat at a further point of the travel of the sheet.

2. The invention according to claim 1, each of said heating stations comprising oppositely disposed extended electrodes from the opposite sides of said sheet, and means for supplying controlled radio-frequency energy to said electrodes.

3. The invention according to claim 2, including static neutralizing means comprising means for sensing an electric charrge 0n the surface of said web subsequent to its leaving the second heating station, and neutralizing electrode means for selectively supplying a neutralizing charge to said surface of opposite polarity from said sensed charge to electrically neutralize said web.

4. The invention according to claim 3, said static neutralizing means comprising two oppositely oriented gridcontrolled vacuum tubes connected in parallel between one terminal of a source of high tension alternating cur rent and said ncutralizer electrode means; and separate connections from said charge sensing means to the respcctive grids of said vacuum tubes arranged to alternatively block current flow in one of said tubes for each polarity of charge detected by the sensing means.

5. The invention according to claim 4, said sensing means comprising two independent sensing stations, each respectively connected to one of said vacuum tubes.

6. A static discharge system for moving web material comprising means for sensing an electric charge on the surface of said web material, and neutralizer electrode means for selectively supplying a neutralizing charge to said surface of opposite polarity from said sensed charge to electrically neutralize said web material.

7. The invention according to claim 6, said static neutralizing means comprising two oppositely oriented gridcontrolled vacuum tubes connected in parallel between one terminal of a source of high tension alternating current and said neutralizer electrode means; and separate connections from said charge sensing means to the respective grids of said vacuum tubes arranged to alternatively block current flow in one of said tubes for each polarity of charge detected by said sensing means.

8. The invention according to claim 7, said sensing means comprising two independent sensing stations, each respectively connected to one of said vacuum tubes.

9. Apparatus for coating a moving web with a finishing material comprising means for continuously moving said web in one direction, spray means for spraying a solution of said finishing material in finely divided form toward a surface of said web during said motion, first electrode means adjacent and surrounding said spray means, second electrode means adjacent the opposite surface of said web, means for impressing a high-potential unidirectional voltage between said first and said second electrode means, to establish a corona discharge, said spray and said corona discharge extending from the region of said spray means toward said web over a surface extending transversely across said sheet; a first heating station extending transversely across said web and spaced in the direction of motion thereof from said spray means for supplying a substantial portion of the heat required to treat the finishing material, means for sensing the resistance to the flow of electric current through said web subsequent to leaving said first heating station, and a second heating station controlled by said sensing means for supplying additional heat at a further point in the travel of the sheet.

10. The invention according to claim 9, said first electrode means being attenuated and so disposed about said spray means as to provide a curtain of corona discharge to confine the spray of finely divided material to a restricted region.

References Cited in the file of this patent UNITED STATES PATENTS 2,125,050 Josephs July 26, 1938 2,221,338 Wintermute Nov. 12, 1940 2,231,457 Stephen Feb. 11, 1941 2,304,983 Winkley Dec. 15, 1942 2,349,300 Olsen May 23, 1944 2,405,249 Wilson Aug. 6, 1946 2,448,008 Baker Aug. 31, 1948 2,484,594 Spangenberg Oct. 11, 1949 2,569,116 Roscoe Sept. 25, 1951 2,615,822 Huebner Oct. 28, 1952 2,658,009 Ransburg Nov. 3, 1953 U 53 DEPARTMENT OF COMMERCE PATENT OFFICE @RTHFECATE QF CORRECTION March ll 1958 Patent N00 2,826,166

Albert SQ Davis, Jr

' It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let cers Patent should read as corrected below.

Golumn 5, lines 3 and. 6 and. eolmnn 6, lines 15 and 24., for "sheet" each occurrence, read vven Signed and sealed. this 20th day of May 1.958a

(SEAL) Attest: KARL E0 AXLINE ROBERT C. WATSON Conmissioner of Patents Attesiiing Officer Uo S, DEPARTMENT OF COMMERCE PATENT OFFICE GERTIFICATE OF CORRECTION March 11, 1958 Patent Noe 2,826,166

Albert So Dennis Jro Iti's hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let cers Patent should read as corrected below. 7

Column. 5,v lines 3 and. 6 and column 6, lines 15 and 2,4, for "sheet", each occurrence, read ===web==-a Signed and. sealed this 20th day of May 1,9580

(SEAL) Atteat: KARL HOiQCLINE ROBERT C. WATSON Attesting Officer Conmissioner of Patents 

